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      <title>如何分析内存使用情况并排查内存泄漏问题 - 交互式测验</title>
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            <div class="quiz-header">
              <h1>如何分析内存使用情况并排查内存泄漏问题 - 交互式测验</h1>
              <p>检验你对文档内容的理解程度</p>
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  {
    "question": "在排查Java内存泄漏时，哪个命令行工具的主要功能是生成Java堆转储（heap dump）文件，以便后续使用如Eclipse MAT等工具进行离线分析？",
    "options": [
      "jstat",
      "jmap",
      "jconsole",
      "top"
    ],
    "correctAnswerIndex": 1,
    "explanation": "根据文档，`jmap` 是一个用于生成Java堆转储的工具。堆转储文件是内存泄漏分析的基础，它捕获了特定时刻JVM堆内存的快照，可以被MAT等工具加载以分析对象引用关系和查找泄漏源。`jstat`用于监控GC统计信息，`jconsole`是图形化监控工具，而`top`是系统级的进程监控工具。",
    "source": "文档中「内存泄漏的诊断工具」部分的「1.1. jmap」",
    "hint": "思考一下，哪一个工具是用来“制作”一个内存快照文件，而不是实时“观察”内存状态的？"
  },
  {
    "question": "在使用Linux的 `free -m` 命令查看内存时，输出中的 `available` 字段代表什么？",
    "options": [
      "系统中物理内存的总量。",
      "完全未被使用的物理内存量。",
      "当前可供应用程序启动和运行的内存量，它考虑了可以被回收的缓存和缓冲区内存。",
      "仅用于文件系统缓存和IO缓冲区的内存量。"
    ],
    "correctAnswerIndex": 2,
    "explanation": "文档中明确解释，`available` 字段指的是当前可用的内存量，它不仅包括完全空闲的内存（free），还包括了那些虽然被用作缓存（buff/cache）但可以在需要时被系统回收以供应用程序使用的部分。因此，它是评估系统可用内存更准确的指标。",
    "source": "文档中「使用系统工具分析内存使用」部分的「1. free 命令」",
    "hint": "这个指标比单纯的 `free` 内存更能真实地反映系统还能“挤出”多少内存给新程序使用。"
  },
  {
    "question": "Eclipse Memory Analyzer Tool (MAT) 在内存泄漏诊断流程中扮演了什么关键角色？",
    "options": [
      "实时监控JVM的垃圾回收活动。",
      "对Java代码进行静态分析，自动发现潜在的内存泄漏风险。",
      "分析由`jmap`等工具生成的堆转储文件，帮助识别内存泄漏的根源和对象引用链。",
      "作为图形化界面实时连接到运行中的JVM，展示内存使用趋势图。"
    ],
    "correctAnswerIndex": 2,
    "explanation": "MAT是一个强大的离线分析工具，其核心功能是加载和分析Java堆转储文件（.hprof）。通过其“泄漏怀疑报告”（Leak Suspects Report）和“支配树”（Dominators View）等功能，可以深入分析对象间的引用关系，从而精确定位导致内存无法被回收的根本原因。",
    "source": "文档中「内存泄漏的诊断工具」部分的「2.1. Eclipse Memory Analyzer Tool (MAT)」",
    "hint": "这个工具的作用是在问题发生后进行“事后分析”，而不是“实时监控”。"
  },
  {
    "question": "根据文档，以下哪项是预防内存泄漏的最佳编码实践之一？",
    "options": [
      "手动频繁调用 `System.gc()` 来强制进行垃圾回收。",
      "为JVM设置尽可能大的堆内存空间。",
      "使用 `try-with-resources` 语法来确保实现了`AutoCloseable`接口的资源（如文件流、数据库连接）被自动关闭。",
      "在静态集合中缓存所有常用对象以提高性能。"
    ],
    "correctAnswerIndex": 2,
    "explanation": "文档在预防部分强调了资源管理的重要性，并明确推荐使用Java 7引入的`try-with-resources`语法。这种方式可以确保资源在使用完毕后无论是否发生异常都会被正确关闭，从而有效避免因资源未释放而导致的内存泄漏。在静态集合中存储对象反而是一个常见的泄漏模式。",
    "source": "文档中「监控与预防」部分的「2.1. 编码实践」",
    "hint": "文档中提到了一个Java 7及以后版本提供的、可以自动管理资源关闭的语法结构。"
  },
  {
    "question": "哪个Linux命令可以用来查看特定进程的内存映射（memory map），详细展示其地址空间中各个内存段的地址、大小、权限和映射文件？",
    "options": [
      "vmstat",
      "free",
      "pmap",
      "top"
    ],
    "correctAnswerIndex": 2,
    "explanation": "`pmap <pid>` 命令专门用于报告指定进程的内存映射。它的输出对于深入诊断单个进程的内存使用情况非常有用，可以清晰地看到哪些库文件被加载，以及堆、栈等内存区域的分布情况。",
    "source": "文档中「使用系统工具分析内存使用」部分的「4. pmap 命令」",
    "hint": "这个命令的名称是 “process memory map” 的缩写。"
  },
  {
    "question": "在分析一个进程的内存占用时，`smem` 工具提供了多个指标。其中哪个指标表示进程“独占”的、不与任何其他进程共享的内存大小？",
    "options": [
      "PSS (Proportional Set Size)",
      "RSS (Resident Set Size)",
      "Swap",
      "USS (Unique Set Size)"
    ],
    "correctAnswerIndex": 3,
    "explanation": "文档对 `smem` 的输出进行了解释，其中USS (Unique Set Size) 指的是一个进程使用的唯一内存量。这部分内存如果该进程终止，就会被完全释放。相比之下，RSS是进程实际占用的物理内存（包含共享部分），而PSS是按比例计算共享内存后的结果。",
    "source": "文档中「使用系统工具分析内存使用」部分的「5. smem 命令」",
    "hint": "这个指标的关键词是“唯一”（Unique）。"
  },
  {
    "question": "文档中提到了多种内存泄漏的典型表现，以下哪项最符合其描述？",
    "options": [
      "应用程序启动速度异常缓慢。",
      "系统响应逐渐变慢，长时间运行后内存使用率持续上升，并可能最终导致 `OutOfMemoryError` 崩溃。",
      "网络连接频繁中断，但内存使用保持稳定。",
      "CPU使用率瞬间达到100%后恢复正常。"
    ],
    "correctAnswerIndex": 1,
    "explanation": "内存泄漏的典型特征是一个渐进的过程。随着时间推移，未被释放的内存对象越积越多，导致可用内存越来越少，垃圾回收（GC）越来越频繁且效果不佳，最终系统性能下降，直至内存耗尽而崩溃。这是一个缓慢累积的过程，而非瞬时问题。",
    "source": "文档中「内存泄漏的识别」部分的「1. 理解内存泄漏的表现」",
    "hint": "内存泄漏通常不是一个“突发”事件，而是一个“慢性病”。"
  }
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                reportEl.remove();
            }
            quizContentEl.insertAdjacentHTML('beforeend', finalScoreHtml);
            document.getElementById('review-btn').addEventListener('click', reviewQuiz);
        }

        function reviewQuiz() {
            const reportEl = document.querySelector('.final-score-container');
            if (reportEl) {
                reportEl.remove();
            }

            document.querySelector('.quiz-body').style.display = 'block';
            document.getElementById('quiz-footer').style.display = 'flex';
            
            currentQuestionIndex = 0;
            loadQuestion();
            updateNavigationButtons(); // Ensure nav buttons are correctly displayed
        }

        // Event Delegation for options
        optionsListEl.addEventListener('click', (event) => {
            if (event.target && event.target.matches('li.option-item')) {
                // Check if the question has already been answered
                if (userAnswers[currentQuestionIndex] === null) {
                    const selectedIndex = parseInt(event.target.dataset.index, 10);
                    selectOption(selectedIndex);
                }
            }
        });

        prevBtn.addEventListener('click', goToPreviousQuestion);
        nextBtn.addEventListener('click', goToNextQuestion);
        hintBtn.addEventListener('click', showHint);
        
        // 初始加载
        loadQuestion();
      </script>
    </body>
    </html>
  